The present invention relates to a single-layer or multi-layer packaging film or sheet having a layer of a polyamide resin composition, and more particularly to packaging films or sheets which are well balanced among properties such as formability, heat shrinkability, gas barrier properties, softness and suitability for automatic packaging machines equipped with a sealing mechanism such as a high-frequency sealer.
The packaging films or sheets according to the present invention are particularly suitable for use as casing films, pillow packaging films or sheets and deep-draw packaging films or sheets for filling and packaging fluid or semifluid foods such as sausage and solid foods such as processed meat and ham.
In recent years, remarkable technical innovation has been made in the field of food packaging, and packaging materials most suitable for packaging, preservation, shipment and the like of various foods have been always demanded. The development of an automatic packaging system has been advanced with a view toward increasing production and reducing cost, and so the packaging materials are required to have excellent suitability for automatic packaging machines.
Single-layer or multi-layer films or sheets formed of various kinds of synthetic resins are generally used in the fields of casing films, pillow packaging films or sheets and deep-draw packaging films or sheets for filling and packaging fluid or semifluid foods, for example, processed livestock products such as sausage, processed marine products such as fish meat sausage, and processed farm products and cooked products such as devil""s-tongue jelly and sweet rice jelly, and solid products such as processed meat products and ham. For example, films formed of a resin composition composed of nylon and a polyolefin resin, or multi-layer laminated films composed of a nylon layer and a polyolefin resin layer are often used in the field of the casing films.
Of these films, a multi-layer laminated film composed of a nylon layer and a polyethylene layer (hereinafter referred to as xe2x80x9cNy/PE filmxe2x80x9d) has good heat sealing property and gas barrier properties and is hence widely used. However, this Ny/PE film has involved a problem that it is lacking in softness. In addition, to the Ny/PE film, may be applied fin sealing (sealing surfaces being both the polyethylene layer) in which the polyethylene layer is used as sealing layers, but can not be applied the so-called overlap sealing (the sealing surfaces being the nylon layer and polyethylene layer). Therefore, the Ny/PE film can not be applied to any automatic filling and packaging machine equipped with an envelope-seam type sealing mechanism.
Several proposals have been made for polyamide resin compositions satisfying various properties as a casing film by a single layer. For example, in Japanese Patent Application Laid-Open No. 122732/1992, has been proposed a casing film formed from a mixture of nylon 6, and an aromatic copolyamide (hereinafter referred to as xe2x80x9cnylon 6I/6Txe2x80x9d) composed of a polycondensate of hexamethylenediamine with terephthalic acid and isophthalic acid. However, this casing film has involved difficulty in stably conducting blow stretching when this casing film is produced by blown-film extrusion, because the internal stress of a tubular parison upon the blow stretching is high, so that the air pressure within a blown bubble becomes high, and bubble break often occurs. In addition, this casing film has also involved a problem that when the casing film is filled with sausage in accordance with a method known per se in the art, boiled and then cooled, the wrinkles occur on the surface of the product, and the dimensions of the product become unstable. Further, the casing film has high stiffness, so that working properties such as shirring and ease of filling are deteriorated.
When an aromatic nylon (hereinafter referred to as xe2x80x9cnylon MXD6xe2x80x9d) composed of adipic acid and m-xylylene-diamine is used in place of the nylon 6I/6T in the polyamide resin compositions, the above-described tendency becomes more pronounced. A film or sheet obtained by blown-film extrusion using the nylon MXD6 involves difficulty in deep drawing it because when it is deep drawn, elongation of the film or sheet becomes uneven at portions corresponding to parts of from corners of the bottom to side walls of a deep-draw mold.
It is an object of the present invention to provide a single-layer or multi-layer packaging film or sheet having excellent formability, heat shrinkability, gas barrier properties and softness.
Another object of the present invention is to provide a single-layer or multi-layer packaging film or sheet which has excellent ease of filling, causes no wrinkle and has excellent dimensional stability when it is used as a casing film.
A further object of the present invention is to provide a single-layer or multi-layer packaging film or sheet which has such excellent properties as described above and is suitable for use as a casing film, a pillow packaging film or sheet, or a deep-draw packaging film or sheet for packaging fluid or semifluid food, or solid food.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art. As a result, it has been found that when a polyamide resin composition comprising a specific copolymer nylon is used for a single-layer or multi-layer packaging film or sheet having a layer formed of a polyamide resin composition, the above objects can be achieved.
The packaging films or sheets according to the present invention may be used in the form of a single-layer film or sheet, but may be used in the form of a multi-layer film or sheet by laminating it on other layers such as a polyolefin resin layer, as desired. The single-layer films composed of a layer of the polyamide resin composition according to the present invention or the multi-layer films having the layer of the polyamide resin composition as a surface layer have excellent suitability for automatic packaging machines equipped with a high-frequency sealing mechanism and may also be ultrasonically sealed.
The packaging films or sheets according to the present invention can be suitably used as heat shrinkable films, in particular, casing films when they are formed into oriented films. A multi-layer film or sheet obtained by laminating a polyolefin resin layer on the layer of the polyamide resin composition can be heat sealed by using the polyolefin resin layer as a sealing surface. A single-layer or multi-layer tubular film or sheet obtained by blown-film extrusion can be used as a casing film as it is. Non-oriented packaging films or sheets according to the present invention have excellent suitability for automatic packaging machines and deep drawing property and are suitable for use as films or sheets for pillow packaging (i.e., flow-pack) and deep-draw packaging (i.e., thermo-forming).
The present invention has been led to completion on the basis of these findings.
According to the present invention, there is thus provided a single-layer or multi-layer packaging film or sheet having at least one layer formed of a polyamide resin composition, wherein the layer formed of the polyamide resin composition is a layer (A) formed of a polyamide resin composition comprising a copolymer nylon (c) composed of an aliphatic nylon (co)polymer component (1) and an aromatic nylon (copolymer component (2) in a proportion of at least 5 wt.%.
Copolymer nylon (c):
In the present invention, as a polyamide resin composition for forming the polyamide resin composition layer (A), is used a polyamide resin composition comprising a copolymer nylon (c) composed of an aliphatic nylon (co)polymer component (1) and an aromatic nylon (co)polymer component (2) in a proportion of at least 5 wt. %.
Examples of the aliphatic nylon (co)polymer component (1) include nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 6/66 and nylon 6/12. Of these, at least one aliphatic nylon (co)polymer component selected from the group consisting of the components of nylon 6, nylon 66 and nylon 610 is preferred. Particularly, nylon 6/12, nylon 66/69, nylon 66/610 and nylon 610 are more preferred.
As the aromatic nylon (co)polymer component (2), is preferably used that having an aromatic diamine unit or that having an aromatic dicarboxylic acid unit. Specific examples thereof include xylylene type polyamides. The xylylene type polyamides are polyamide resins synthesized by a polycondensation reaction of m-xylylenediamine alone or a diamine mixture of m-xylylenediamine in an amount of at least 60 wt. %, preferably at least 70 wt. % and p-xylylenediamine in an amount of at most 40 wt. %, preferably at most 30 wt. % with an aliphatic dibasic acid having 6-12 of carbon atoms, for example, adipic acid, sebacic acid, suberic acid, undecanedioic acid or dodecanedioic acid. More specific examples thereof include homopolymers such as poly(m-xylylene adipamide), poly(m-xylylene sebacamide) and poly(m-xylylene suberamide), m-xylylene/p-xylylene adipamide copolymers, m-xylylene/p-xylylene pimelamide copolymers, m-xylylene/p-xylylene azelamide Copolymers. and m-xylylene/p-xylylene adipamide/sebacamide copolymers. Of these, poly(m-xylylene adipamide) (MXD6) is preferred.
Other examples of the aromatic nylon (co)polymer component (2) include polycondensates of hexamethylene-diamine with at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid and isophthalic acid.
A proportion of the aromatic nylon (co)polymer component (2) to be copolymerized in the copolymer nylon (c) is preferably at most 40 wt. % from the viewpoints of formability, heat shrinkability, gas barrier properties and softness.
Preferable examples of the copolymer nylon (c) include copolymer nylons comprising {circle around (1)} 45-92 wt. % of a nylon 6 component and {circle around (2)} 4-25 wt. % of another aliphatic nylon component than the nylon 6 component as the aliphatic nylon (co)polymer component, and {circle around (3)} 4-40 wt. % of an aromatic nylon component containing a xylylenediamine unit as the aromatic nylon (co)polymer component. A specific example thereof includes nylon 6/12/MXD6.
Other preferable examples of the copolymer nylon (c) include copolymer nylons comprising {circle around (1)} 60-96 wt. % of a nylon 610 component or a nylon 66/610 component as the aliphatic nylon (co)polymer component and {circle around (2)} 4-40 wt. % of an aromatic nylon component containing a xylylenediamine unit as the aromatic nylon (co)polymer component. Specific examples thereof include nylon 610/MXD6 and nylon 66/610/MXD6.
Further examples of the copolymer nylon (c) include copolymer nylons comprising {circle around (1)} 60-96 wt. % of a nylon 6 component or a nylon 66/69 component as the aliphatic nylon (co)polymer component and {circle around (2)} 4-40 wt. % of a polycondensate component of hexamethylenediamine with at least one aromatic dicarboxylic acid selected from the group consisting of isophthalic acid and terephthalic acid as the aromatic nylon (co)polymer component. Specific examples thereof include nylon 6/6I and nylon 66/69/6I.
The copolymer nylon (c) used in the present invention is a crystalline polyamide and generally has a crystallization velocity, xcfx84xc2xd of 20 seconds or longer. When the so-called hot stretching, in which a polyamide resin composition is heated to 70-95xc2x0 C. to stretch it, is conducted, the incorporation of the copolymer nylon (c) into the polyamide resin composition permits slowing the crystallization velocity of the polyamide resin composition to facilitate the operation of the hot stretching. Namely, the copolymer nylon (c) contributes to the improvement of stretchability, film-forming property and high-frequency sealing property. This copolymer nylon also permits improvement in the softness of a film or sheet formed, thereby improving its ease of filling with sausage or the like and further its secondary processing characteristics or properties such as suitability for shirring, ring-forming property, ease of film cutting, suitability for pillow packaging machines and deep-drawing property. The copolymer nylon improves the gas barrier properties of the film or sheet to some extent. Any blend of an aliphatic nylon such as nylon 6 and an aromatic nylon, not the copolymer nylon, cannot well balance these features with one another.
A proportion of the aromatic nylon (co)polymer component (2) such as nylon MXD6 to be copolymerized in the copolymer nylon (c) is at most 40 wt. %, preferably 4-40 wt. %. If the proportion is too low, the oxygen gas barrier property of the resulting film or sheet is lowered. If the proportion is too high on the other hand, the stiffness of the film or sheet becomes too high, and so its softness is impaired. If a proportion of the aliphatic nylon (co)polymer component (1) to be copolymerized in the copolymer nylon (c) is too low, the softness of the resulting film or sheet is impaired. If the proportion is too high on the other hand, the effects of improving the oxygen transmission rate and water vapor transmission rate of the film or sheet are lessened.
In the copolymer nylon (c) having a copolymerization composition of aliphatic nylon/another aliphatic nylon/ aromatic nylon copolymer such as the nylon 6/12/MXD6 and the nylon 66/610/MXD6, the presence of another aliphatic nylon component permits improvement in the softness of the resulting film or sheet. When the ordinary nylon MXD6 is used in place of the specific copolymer nylon, the resulting film becomes poor in softness and stretchability, is too hard to achieve good suitability for shirring as a casing film for packaging a pasty substance such as sausage, and is also not very improved in dimensional stability.
A proportion of the copolymer nylon (c) to be incorporated into the polyamide resin composition is at least 5 wt. %, preferably 5-40 wt. %, more preferably 5-30 wt. %. If the proportion is too low, the effect of slowing the crystallization velocity of the polyamide resin composition is lessened. If the proportion is too high on the other hand, the resulting film becomes too soft, so that when a casing film composed of such a film is filled with sausage or the like, the film is elongated by the filling pressure, and so the dimensions and form of the resulting product vary, and the dimensional stability and form stability of the product are impaired. Even if the proportion of the copolymer nylon (c) exceeds 40 wt. %, such various properties are easy to be well balanced when a layer of such a composition is laminated on a layer of another polyamide resin than this, for example, an aliphatic (copolymer nylon or nylon MXD6.
Polvamide resin composition:
According to the present invention, in a single-layer or multi-layer packaging film or sheet having at least one layer formed of a polyamide resin composition, a polyamide resin composition comprising the copolymer nylon (c) in a proportion of at least 5 wt. % is used as the polyamide resin composition for forming the layer of the polyamide resin composition. The polyamide resin composition comprises at least 5 wt. % of the copolymer nylon (c) and at most 95 wt. % of another nylon (co)polymer than the copolymer nylon (c), and as needed, any other resin component such as an amorphous nylon (b) and/or a polyolefin resin may be blended therewith within the limits of a minor amount.
As the polyamide resin composition, is preferred a polyamide resin composition comprising 40-70 wt. % of nylon 6 (a), 5-20 wt. % of an amorphous nylon (b), 5-30 wt. % of the copolymer nylon (c) and 10-30 wt. % of a polyolefin resin (d).
Besides, a polyamide resin composition comprising 50-95 wt. % of nylon 6 (a) and 5-50 wt. % of the copolymer nylon (c) may be used as the polyamide resin composition. Further, a polyamide resin composition comprising 50-95 wt. % of nylon MXD6 (e) and 5-50 wt. % of the copolymer nylon (c) may preferably be used as the polyamide resin composition.
Nylon 6:
Nylon 6 (Ny 6) in the polyamide resin composition is concerned in the balance between film-forming property and oxygen gas barrier property. A proportion of nylon 6 to be incorporated may be suitably determined according to other blending components. In a polyamide resin composition comprising nylon 6 (a), an amorphous nylon (b), the copolymer nylon (c) and a polyolefin resin (d), however, the proportion of the nylon 6 is generally 40-70 wt. %, preferably 50-70 wt. %.
In a polyamide resin composition comprising nylon 6 (a) and the copolymer nylon (c), the proportion of the nylon 6 is generally 50-95 wt. %, preferably 40-95 wt. %. Accordingly, the proportion of the copolymer nylon (c) is generally 5-50 wt. %, preferably 5-40 wt. %.
If the proportion of nylon 6 is too high, the oxygen transmission rate and water vapor transmission rate of the resulting oriented film are lowered. If the proportion is too low on the other hand, the stretchability upon the formation of a blown film is lowered.
Amorphous nylon:
The amorphous nylon in the polyamide resin composition is a polyamide having an aromatic ring in its main chain and/or side chain and having no crystallinity or very low crystallinity. Specific examples thereof include polycondensates of a dicarboxylic acid such as terephthalic acid or isophthalic acid with a diamine such as hexamethylenediamine or copolymers thereof. For example, polyamides (nylon 6I/6T) obtained by polycondensing a dicarboxylic acid component composed of 10-50 wt. % of terephthalic acid and 90-50 wt. % of isophthalic acid with hexamethylenediamine may be mentioned.
The stretchability and oxygen gas barrier property of the polyamide resin composition is affected by the range of the amorphous nylon in the polyamide resin compositon. A proportion of the amorphous nylon to be incorporated in the polyamide resin composition is generally 5-20 wt. %, preferably 5-15 wt. %. If the proportion of the amorphous nylon is too high, the stiffness of the resulting film becomes high, and so its softness is lowered. If a film does not have sufficient softness, difficulty is encountered on handling when the film is put to practical use as a casing film to fill it with sausage or the like, and since suitability for shirring and ring-forming property are deteriorated, or the life of a cutter for cutting the film is shortened, problems arise on secondary processing properties of the film. When it is combined with a specific copolymer composition, these properties are easy to be well balanced. If the proportion of the amorphous nylon is too low, it is difficult to satisfactorily retain the form of the resulting film.
Polyolefin resin:
Examples of the polyolefin resin used in the present invention include homopolymers of ethylene and xcex1-olefins, such as high density polyethylene, medium density polyethylene, low density polyethylene and polypropylene; ethylene-xcex1-olefin copolymers (for example, copolymers obtained by using a metallocene catalyst, such as AFFINITY(trademark)) such as linear low density polyethylene (LLDPE) and very low density polyethylene (VLDPE); and besides ionomer resins, polyamide-modified ionomer resins, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-methyl acrylate copolymers, ethylene-methyl methacrylate copolymers and ethylene-methacrylic acid copolymers. These polyolefin resins may be used either singly or in any combination thereof.
As the polyolefin resin mixed with the polyamide resin composition, ethylene copolymers such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, and polyamide-modified ionomer resins are preferred from the viewpoint of compatibility with the individual polyamide components.
The polyamide-modified ionomer resins are resins obtained by ionizing a copolymer of ethylene and an xcex1,xcex2-unsaturated carboxylic acid with a metal ion such as zinc, lithium, potassium, magnesium, calcium or sodium ion to prepare an ionomer, adding a polyamide to the ionomer and melting and kneading the resultant mixture at a high temperature of 200-350xc2x0 C. to modify the ionomer. Examples of the polyamide used herein include nylon 6, nylon 66, nylon 6/66, nylon 6/10, nylon 6/12, nylon 11, nylon 12 and mixture of two or more of these polyamides. Of these, nylon 6 and copolymers thereof are preferred.
A proportion of the polyolefin resin to be incorporated in the polyamide resin composition is generally 10-30 wt. %. If the proportion of the polyolefin resin is too low, the water vapor transmission rate of the resulting film becomes too high, so that loss in weight of the contents in a packaged product becomes great when sausage or the like is packaged with the film to store it. If the proportion is too high, the stretchability of the resulting film is deteriorated, and moreover its oxygen transmission rate is increased, so that the contents in a product packaged with the film tend to undergo putrefaction due to oxidative deterioration.
Film or sheet:
The polyamide resin composition useful in the practice of the present invention can be prepared by mixing the individual components by a method known per se in the art. For example, raw materials such as pellets, granules, powders or the like of the individual polymers are mixed upon the formation of a film or sheet, whereby a uniform composition can be prepared. To the polyamide resin composition, may be added various additives such as a plasticizer, a stabilizer, a lubricant, an antioxidant, a pigment and a dye, as needed, within limits not impairing the properties of the resulting film.
No particular limitation is imposed on the film-forming process. For example, T-die extrusion or blown-film extrusion may be used. The blown-film extrusion is generally used. The melting temperature of each resin is generally 300xc2x0 C. or lower, preferably 240-280xc2x0 C., more preferably 240-260xc2x0 C. A non-oriented film obtained by the T-die extrusion is biaxially oriented simultaneously or successively at an orientation temperature of 120xc2x0 C. or lower by a tenter process. A tubular parison obtained by the blown-film extrusion is biaxially oriented by blowing air into the parison at an orientation temperature of 120xc2x0 C. or lower to inflate it. The draw ratio is generally 2.0-10.0 times, preferably 2.2-8.0 times, more preferably 2.2-5.0 times in each of machine and transversal directions. Moderate heat shrinkability and dimensional stability such as creep characteristics are achieved by the orientation.
The thickness of the film according to the present invention is generally 10-100 xcexcm, preferably 10-50 xcexcm, more preferably 20-40 xcexcm in the case of a singly-layer film. A thickness too small is not preferable because the oxygen gas barrier property and water vapor barrier property of the film are lowered. A thickness too great is also not preferable because the stiffness of the film becomes too high, and so its softness is deteriorated. In the case of a multi-layer film, the film is used in a thickness ranging from 10 to 250 xcexcm.
In the packaging of processed meat products, packaged products such as sausage dislike wrinkling from the viewpoint of the aesthetic appearance of the products. In order to prevent the products from wrinkling, it is necessary for the film to shrink under heat upon boiling or sterilization treatment so as to keep it tense. The oriented films according to the present invention have a shrink (hot-water shrink) of generally at least 5%, preferably at least 8%, more preferably at least 10% in each of longitudinal and transversal directions when immersed in hot water of 80xc2x0 C.
The films according to the present invention preferably have a haze of at most 20%. Since the haze of the films is low, the contents such as sausage can be visually seen from the outside of the packaging film.
The films or sheets according to the present invention have an oxygen transmission rate (in terms of the thickness of 35 xcexcm) of 300 cm3/m2xc2x7dayxc2x7atm or smaller, preferably 200 cm3/m2xc2x7dayxc2x7atm or smaller as measured at a temperature of 30xc2x0 C. and 100% RH (relative humidity) and a water vapor transmission rate of preferably 70 g/m2xc2x7day or smaller as measured at a temperature of 40xc2x0 C. and 90% RH, so that when a food product packaged with the film is stored for a long period of time, putrefaction of the contents by oxygen and loss in weight of water can be prevented, and the flavor and taste of the contents can be retained.
If the hot-water shrink of the casing film according to the present invention is lower than 5t at 80xc2x0 C., a product obtained by filling the casing film with, for example, fluid or semifluid sausage wrinkles in its surface after boiling it. Therefore, such a low hot-water shrink is not preferable.
Hot-water creep at 80xc2x0 C. for 10 seconds may be used as an evaluation standard for the dimensional stability of the films. The oriented films according to the present invention preferably have a hot-water creep of at most 20%, more preferably at most 18%. If the hot-water creep of the film is too high, a dimensional scatter of a packaged product obtained by filling with, for example, sausage becomes too wide after boiling the package. Therefore, such a too high hot-water creep is not preferable.
The films or sheets according to the present invention have excellent high-frequency sealing property. A number of films formed of a resin composition composed of a polyamide and a polyolefin resin and/or the like have heretofore been proposed and used. However, none of them are not particularly referred to the high-frequency sealing property. The present inventors have carried out an extensive investigation as to this sealing property. As a result, it has been found that when a film formed of a polyamide alone, for example, a film of nylon 6, is subjected to high-frequency sealing by an automatic filling and packaging machine (Automatic Filling and Packaging Machine KAP manufactured by Kureha Chemical Industry Co., Ltd.), discharge occurs at the sealed portion, and so good sealing property cannot be achieved. On the other hand, even when a film or sheet formed of the polyamide resin composition according to the present invention is subjected to high-frequency sealing by means of an automatic filling and packaging machine equipped with a high-frequency sealing mechanism, stable sealing can be continuously conducted without discharge. The films or sheets according to the present invention have not only excellent high-frequency sealing property but also good heat sealing property and ultrasonic sealing property.
The films or sheets according to the present invention may be used in the form of a single-layer film or sheet, but may be used in the form of a multi-layer film or sheet by laminating it on, for example, at least one polyolefin resin layer (may be combined with an adhesive resin layer) by co-extrusion or lamination in order to impart or improve heat sealing property.
More specifically, examples of the multi-layer film or sheet include multi-layer films or sheets having a laminated structure of at least 3 layers with an adhesive resin layer (B) and a polyolefin resin layer (C) laminated on a layer (A) of the polyamide resin composition in suitable combinations, for example, A/B/C, A/C/A, A/B/A, C/A/C, A/B/C/B/A and C/B/A/B/C. Additional resin layers may be provided as desired. Of these, the multi-layer film or sheet having a layer (A) of the polyamide rein compositon as a surface layer can be applied to high-frequency sealing.
Examples of the polyolefin resin include homopolymers such as low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE) and polypropylene; ethylene-xcex1-olefin copolymers (for example, copolymers obtained by using a metallocene catalyst, such as AFFINITY(trademark); particularly, those having a density of 0.900 g/cm3 or higher) such as linear low density polyethylene (LLDPE) and very low density polyethylene (VLDPE); ethylene copolymers such as ethylene-vinyl acetate copolymers (EVA), ethylene-ethyl acrylate copolymers (EEA), ethylene-methacrylic acid copolymers (EMA), ethylene-acrylic acid copolymers (EAA) and ionomer resins; and mixtures composed of two or more of these polymers.
Examples of the adhesive resin include modified polymers obtained by graft-copolymerizing an unsaturated carboxylic acid such as maleic acid, fumaric acid or acrylic acid, or an anhydride or ester thereof with homopolymers or copolymers of olefins, such as polyethylene resins (including xcex1-olefin resins such as LLDPE and VLDPE), polypropylene, polybutene, copolymers of these comonomers with each other, ionomer resins, ethylene-acrylic acid copolymers and ethylene-vinyl acetate copolymers; and mixtures of two or more of these graft copolymers.
Examples of other resin layers and additional resin layers include a layer formed of a saponified product (EVOH) of an ethylene-vinyl acetate copolymer, and layers formed of gas barrier resins such as nylon MXD6. These gas barrier resin layers are generally provided as an intermediate layer in the multi-layer films or sheets. In this case, in order to enhance the film-forming property and stretchability of the gas barrier resin, it is preferable that {circle around (1)} the gas barrier resin layer be provided in adjacency with the polyamide resin composition layer (A), {circle around (2)} the gas barrier resin layer be provided between two layers (A) of the polyamide resin composition, or {circle around (3)} in the case of nylon MXD6, it be blended with the copolymer nylon (c) to use the blend to form a polyamide resin composition layer (A).
As other resin layers and additional resin layers, may also be mentioned layers of other polyamide resins and layers of polyethylene terephthalate resins.
As the multi-layer packaging films or sheets according to the present invention, may be mentioned multi-layer oriented films or sheets comprising at least one polyamide resin composition layer (A), and multi-layer non-oriented films or sheets comprising at least one polyamide resin composition layer (A).
Specifically, multi-layer packaging films or sheets comprising at least one polyamide resin composition layer (A) as an intermediate layer may be mentioned. More specifically, multi-layer packaging films or sheets comprising at least one polyamide resin composition layer (A) as an intermediate layer and polyolefin resin layers as the outermost layer and the innermost layer through adhesive layers may be mentioned.
Besides, multi-layer packaging films or sheets comprising at least one polyamide resin composition layer (A) as an intermediate layer, a polyethylene terephthalate resin layer as one surface layer through an adhesive layer, and a polyolefin resin layer as the other surface layer through an adhesive layer may be mentioned. In order to control the slip property of the resulting multi-layer film or sheet, silica particles may be added to the polyethylene terephthalate resin of the surface layer. As a method for adding the silica particles, there is a method in which 2.5 wt. % of silica particles are blended with 97.5 wt. % of a polyethylene terephthalate resin to prepare a lubricant, and the lubricant is added to a polyethylene terephthalate resin. If the concentration of the silica particles in the resin is 1,000 ppm or higher, the suitability of the resulting film or sheet for pillow packaging becomes poor. Therefore, it is preferable to control the concentration to generally about 200-800 ppm, more preferably about 500 ppm. A multi-layer film or sheet comprising, as a surface layer, the polyethylene terephthalate resin layer the slide property of which has been controlled as described above has far excellent suitability for pillow packaging.
Examples of the intermediate layer include {circle around (1)} a layer having a layer structure composed of at least one polyamide resin composition layer (A) and at least one polyamide layer laminated in adjacency with each other, and {circle around (2)} a layer having a layer structure composed of at least one polyamide resin composition layer (A) and at least one gas barrier resin layer laminated in adjacency with each other.
Multi-layer packaging films or sheets comprising at least one polyamide resin composition layer (A) as at least one surface layer may be mentioned. In this case, a polyolefin resin layer may be provided as an intermediate layer, or a layer of another polyamide resin (including another polyamide resin composition) may be provided as the other surface layer. More specifically, multi-layer packaging films or sheet comprising a polyamide resin composition layer (A) as one surface layer, and a polyamide resin layer as the other surface layer may be mentioned.
Multi-layer packaging films or sheets having a layer structure composed of at least two layers of a layer formed of the copolymer nylon (c) composed of the aliphatic nylon (co)polymer component (1) and the aromatic nylon (co)polymer component (2), and a layer formed of another polyamide than the copolymer nylon (c) in adjacency with each other may also exhibit good various properties. Examples of thereof include aliphatic nylon (co)polymer layer/adhesive resin layer/copolymer nylon (c) layer/adhesive resin layer/polyethylene layer, mixed layer of aliphatic nylon (co)polymer and amorphous nylon (b)/adhesive layer/copolymer nylon (c) layer/adhesive resin layer/mixed layer of polyethylene and anti-clouding agent.
Multi-layer packaging films or sheets having a layer structure composed of at least two layers of a layer formed of the polyamide resin composition comprising the copolymer nylon (c) composed of the aliphatic nylon (co)polymer component (1) and the aromatic nylon (co)polymer component (2) having an aromatic diamine unit, and at least one layer of a layer formed of another polyamide resin composition than the above composition and a gas barrier resin layer may also exhibit good various properties.
The single-layer or multi-layer oriented films or sheets according to the present invention can be suitably used as casing films. Since the films or sheets comprising the polyamide resin composition according to the present invention are good in film-forming property and stretchability upon the formation of the films or sheets and have moderately balanced properties among softness, hot-water shrink, creep property, toughness, gas barrier properties, dimensional stability, suitability for automatic packaging machines and the like, they are suitable for casing films for filling and packaging fluid or semifluid foods, for example, processed livestock products such as ham and sausage, processed marine products such as fish meat sausage, and processed farm products and cooked products such as devil""s-tongue jelly and sweet rice jelly.
The single-layer or multi-layer non-oriented films or sheet according to the present invention are suitably used as films or sheets for deep-draw packaging and pillow packaging.
Blow molded container:
The polyamide resin composition comprising a copolymer nylon (c) composed of an aliphatic nylon (co)polymer component (1) and an aromatic nylon (co)polymer component (2) in a proportion of at least 5 wt. %, and the copolymer nylon (c) itself have excellent moldability, are easy to form a uniform section, and can be suitably used in stretch blow molding in particular.
Therefore, according to the present invention, there are provided single-layer or multi-layer blow molded containers having at least one layer formed of a polyamide resin composition, wherein the layer formed of the polyamide resin composition is a layer (A) formed of a polyamide resin composition comprising a copolymer nylon (c) composed of an aliphatic nylon (Co)polymer component (1) and an aromatic nylon (co)polymer component (2) in a proportion of at least 5 wt. %, or of the copolymer nylon (c) alone.
According to the present invention, there are provided single-layer or multi-layer packaging films or sheets having excellent formability, heat shrinkability, gas barrier properties, softness and suitability for automatic packaging machines equipped with a sealing mechanism such as a high-frequency sealer, heat sealer or ultrasonic sealer. The packaging films or sheets according to the present invention are suitable for use as casing films, pillow packaging films or sheets and deep-draw packaging films or sheets for filling and packaging fluid or semifluid foods such as sausage and solid foods such as processed meat and ham.
The present invention will hereinafter be described more specifically by the following Examples and Comparative Examples. Incidentally, various physical properties in the examples were measured in accordance with the following respective methods.
(1) Crystalline Melting Point (Tm):
The crystalline melting point of each sample was measured by means of a DSC7 (trade name) manufactured by Perkin Elmer Company. The measurement was conducted in the following manner. Namely, 5-10 mg of a sample resin were weighed out, and the resin was melted once and held for 2 minutes at a temperature higher than the melting point at this time by 40xc2x0 C. Thereafter, the resin was quenched to 0xc2x0 C. at a rate of 200xc2x0 C./min and held for 2 minutes. The resin was then heated at a rate of 20xc2x0 C./min, and a melting peak temperature in this process was regarded as the crystalline melting point.
(2) Stretchability (Formability Upon the Formation of an Oriented Film):
A tubular parison was produced with a resin composition sample by blown-film extrusion, and air was blown into the parison to inflate and stretch it, thereby evaluating the sample as to stretchability in accordance with the following standard:
∘: The parison was could be continuously stretched with extremely little breaking of the bubble;
xcex94: Breaking of the bubble sometimes occurred (about once in 8 hours); and
X: Breaking of the bubble frequently occurred (at least two or three times in 8 hours). (3) Shrinkage:
A sample film was immersed for 10 seconds in hot water of 80xc2x0 C., and a shrinkage of the film in each of longitudinal and transversal directions was then determined.
(4) Creep:
A sample film was immersed for 10 seconds in hot water of 80xc2x0 C., and a creep of the film was then determined.
(5) Oxygen Transmission Rate:
The oxygen transmission rate of a sample film was measured by means of MOCON OXTRAN-100 MODEL (trade name) manufactured by MODERN CONTROL Co. under conditions of 30xc2x0 C. and 100% RH in accordance with ASTM D 3985-81.
(6) Water Vapor Transmission Rate:
The water vapor transmission rate of a sample film was measured by means of VAPOR PERMEATION TESTER-400 (trade name) manufactured by LYSSY Co. under conditions of 40xc2x0 C. and 90% RH.
(7) Overfill Rate (Maximum Fill Rate):
A sample casing film was filled with sausage, thereby determining a maximum overfill rate at this time.
(8) Ease of Filling:
Upon the determination of the overfill rate, the ease of filling of the sample casing film was evaluated in accordance with the following standard:
∘: Sausage in the form of semifluid could be smoothly filled into the casing film;
xcex94: The casing film was hard, and its shirring and filling thereinto were hence difficult; and
X: The casing film was elongated, and the dimension in the diametric direction thereof was difficult to retain.
(9) Wrinkling Tendency:
A sample tubular oriented film was filled with sausage, and the resultant product was boiled for 60 minutes in hot water of 80xc2x0 C. and immediately cooled in cold water of 5xc2x0 C., thereby visually observing it and evaluating the film as to the wrinkling tendency in accordance with the following standard:
∘: No wrinkle occurred; and
X: Wrinkles occurred.